There used to be many such applications for GNOME 2, but they can't change the background anymore because they still use GConf, while the background settings are now stored in DConf. And since XML Animated Background Creator is easy to use and install on any Linux distribution, I've upgraded it to work with GNOME 3 (it works with any "shell": Unity, GNOME Shell, fallback session).

To install XML Animated Background Creator, download the Nautilus script, extract it in your home folder and run the following commands in a terminal:

cd ~/XMLBACK
./install.sh

For Fedora, open the install.sh file and replace "gksu" with "beesu" (also, make sure beesu is installed: "sudo yum install beesu").

To create a XML slideshow background, copy all the wallpapers you want to use in your new XML background in a folder, then right click the folder and select Scripts > create xml background.

XML Animated Background Creator will then prompt you to select the time between each wallpaper (5 minutes by default), the transition duration (5 seconds by default), and xml file name. At the end, it also asks you if you want to use the newly generated .xml background file as your wallpaper.

Extra tip: in GNOME 3, you can't select a XML slideshow wallpaper through the Appearance dialog. You don't have to do this manually if you're using XML Background Creator since the script asks you if you want to apply a newly created .xml background file, however, if you want to manually set an XML wallpaper in GNOME 3, use the following command: